You can't remove or disable the built-in developer tools that you find in the Tools menu AFAIK.You would normally open the WebIDE interface via its Shift+F8 shortcut key as shown in the "Tools -> Web Developer" drop-down list.There are some developer toolbox settings (gear icon in the Inspector or any other of the tools), but these apply only to the toolbox and not to the menu.https://developer.mozilla.org/Tools/Too ... x#Settings

If you do not want WebIDE you can remove it entirely as it should show under /tools/addons/extensions.It should also show if typing about:support in the nav text entry.There may also be an accompanying extension- - Valence which can also be removed.HOWEVER, both these extensions leave a number of items enabled in about:config which are not removed.Typing either "webIDE" or "valence" you should be able to find the items.Many are true false toggles along with urls and local local system addresses which can be blanked.